Bioaerosols typically occur in very low concentrations making them very hard to detect. Bioaerosols can be found in the workplace, in residences, in medical facilities, in manufacturing operations, in animal processing facilities, in dairy facilities or other animal houses, in recycling or composting plants, in sanitary landfills, in sewage plants, etc. Airborne microorganisms or bioaerosols can cause disease, allergies, and respiratory problems. Bioaerosols are increasingly feared as being potential bio-warfare and terrorist agents.
There are many aerosol detection and sampling systems. However, most of them are for inert aerosols and their designs do not consider the viability of bioaerosols. Furthermore, they are not capable of distinguishing biological agents from inert agents in the same sample volume.
A known method of detecting and identifying bioaerosols is disclosed in U.S. Pat. No. 6,806,464. An aerosol time-of-flight mass spectrometer using fluorescence techniques is used to ionize selected bioaerosol particles. Laser radiation using a wavelength which is specific to substances affects fluorescence. A fluorescence detector is used to select the bioaerosol particles, and a second laser is used to emit light of a wavelength that effects the ionization of the bioaerosol particles selected by the fluorescence detector. Such a method of detecting and identifying a bioaerosol is rather complex, relying on relatively expensive and complex equipment. Furthermore, the method has not been demonstrated to be able to accurately identify speciation and quantify viable concentration in practical applications.
Other methods for bioaerosol detection rely on impaction or impingement. This is accomplished using inertial forces either by impaction on plates, such as that used in an Anderson Impactor, loaded with agar or by impingement into a liquid, such as that used in an All Glass Impinger or a BioSampler (U.S. Pat. No. 5,902,385). Because inertia is a function of particle size, particle size plays a critical role in determining the ability to sample and quantify bioaerosols; in general, the larger the size, the higher the collection efficiency.
An impactor is a device with nozzles that direct air flow carrying aerosol toward impaction plates. The inertia of the aerosol drives its impaction, and therefore its collection efficiency decreases as aerosol size decreases. The collection efficiency can be increased by applying low pressure or by applying a higher velocity. Unfortunately, this approach dries out agar quickly and therefore cannot be used for collecting viable bioaerosols. Existing viable impactors such as the Anderson Impactor can only collect down to 0.6 μm due to this limitation.
An impinger is a container with nozzles and an aqueous collection medium. Air flow exiting the inlet nozzle(s) form bubbles in the liquid. Aerosol in the bubbles can leave the bubbles due to its inertia, and therefore the collection efficiency decreases as its size decreases. Available impingers such as All Glass Impingers have less than 70% efficiency for particles less than 0.5 μm. The BioSampler, which is an improved version using swirling jets, still has only 80% efficiency for 0.3 μm. As described, either a viable impactor or an impinger has low efficiency for bioaerosols below 0.3 μm. According to Hogan et al. (“Sampling Methodologies and Dosage Assessment Techniques for Submicrometer and Ultrafine Virus Aerosol Particles”, Applied Microbiology, 99, p. 1422-1434, 2005), the efficiency of BioSamplers and All Glass Impingers for collecting MS2 bacteriophage is less than 10%.
Thus, there is a need to overcome these and other problems of the prior art and to provide a high-efficiency viable detecting system for ultrafine bioaerosols.